PLESK license key is invalid?

Hi good people,
I get an invalid license key message when I log in to my Plesk VPS:
"Error: The license key is invalid. In order to use the control panel, please, obtain and install a new fully featured license key.
Your license key has expired. To continue using your control panel, purchase a non-expiring commercial license."

I have asked KH support twice to do something about it and they tried to upgrade it, but each time after they do my domains become inaccessible and I quickly revert to the saved server backup as this is a live business server.

Has anybody encountered the same behavior?

I really need to setup another domain on my VPS and with Plesk locked I cannot move forward.
I dread the thought of manually setting up dns and apache (never done it!) and would love to use Plesk interface for this.

If Plesk has been upgraded, then the license was upgraded for the new version of Plesk - so reverting to an old backup which would be an older version of Plesk would break the licensing as the licenses can't be downgraded. The only option is to upgrade - or migrate to a real control panel like cPanel and away from the leech known as Plesk.